Synthesis, structural elucidation, DNA-binding and anti-oxidant activities of centrosymmetric paddlewheel copper carboxylate complexes

Synthesis, structural elucidation, DNA-binding and anti-oxidant activities of centrosymmetric paddlewheel copper carboxylate complexes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Synthesis, structural elucidation, DNA-binding and anti-oxidant activities of centrosymmetric paddlewheel copper carboxylate complexes Afifa Mushtaq, Muhammad Iqbal, Zahid Rashid, Khadija Shahid, Muhammad Nawaz Tahir, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3960580/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Synthesis, structural characterization and preliminary biological relevance of four new copper carboxylate complexes ( 1 - 4 ) has been presented here. The complexes have been synthesized by direct treatment of the substituted phenyl acetate and pyridine ligands in aqueous medium. The complexes were stable indefinitely with excellent yield and were characterized using spectroscopic and single crystal XRD techniques. FTIR spectroscopy revealed the bridging bidentate coordination mode for the carboxylate moiety in accordance to the actual structure revealed by XRD. Moreover, UV-Visible spectroscopic and cyclic voltammetric studies helped in their characterization and yielded signals which were typical of the copper(II) complexes. Successfully solved single crystal XRD data showed binuclear paddlewheel structures for all the complexes with both copper ions linked through four OCO bridges of ortho-methoxy phenyl acetate ( 1 - 3 ) and ortho-methyl-meta-nitrophenyl acetate ( 4 ). The geometry around each copper was distorted square pyramidal where the apical positions are occupied by meta-bromopyridine ( 1 ), meta-methylpyridine ( 2 ) and DMSO ( 3 and 4 ) molecules. The complexes exhibited excellent DNA-binding activity majorly via intercalation as revealed by four experimental techniques in line with the in silico studies. Their anti-oxidant activity was also comparable to that of the ascorbic acid. Complexes 1 and 4 exhibited significant anti-bacterial activity against Micrococcus luteus and Staphylococcus aureus. These preliminary findings indicated the biological potential of the synthesized complexes. copper(II) paddlewheel complexes structural study DNA-binding anti-oxidant activity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction The continuing importance of metallo-pharmaceuticals in synthetic chemistry research groups is hopeful and necessary for making new advances in the field [1]. Among various parameters used for testing the biological importance of the newly synthesized complexes/drugs is their interaction with DNA. This activity has long been intensely investigated in the pursuit to develop new functional materials for uses in medicine and biotechnology [2]. The DNA-binding activity of the complexes is important since such substances can ultimately develop into agents which will stop the uncontrolled cell division in the tumorous tissues. Several types of compounds are being under investigation to be developed into efficient DNA-binding/cleaving agents. The metal based DNA-binding agents have developmental history dating back to cis-platin which is still the currently used anti-tumor drug, despite numerous well established side effects [3]. The metal based drugs would be hopeful in performing the dual function of interacting with DNA electrostatically through metal ion as well as through the attached ligand moieties. However, since platinum based drugs bind with DNA irreversibly, it has been proposed that the large side effects arising from these drugs might be due to their binding mode. The toxicity has also been attributed to the intrinsic toxicity of the precious platinum metal [3,4]. Therefore, it has been proposed that the preferable binding mode of the drugs with DNA should be non-covalent and reversible type. The non-covalent binding mode has been classified as electrostatic, groove and intercalative binding modes. Keeping in view these points, it is sought that the metal as well as the ligands selected for the synthesis of compounds destined for DNA-binding activity must be non-toxic and harmless to the normal tissues. Additionally, the mode of interaction of the prepared compounds must be preferably non-covalent and reversible [5,6]. In this context, a bio-essential metal will be most preferable with biologically benign ligands. In this context, various substitution derivatives of phenyl acetate have been used as ligands for the synthesis of these complexes which have several preferable features such as small size, water solubility, intermediate Lewis base strength, variable coordinating ability to metal ion. The resulting complexes are expected to have size suitable to permeate easily through biological membranes. The inorganic groups such as nitro and bromo-groups on these ligands promote electrostatic interactions with biological molecules such as DNA. In continuation of our previous work [7,8] we have synthesized copper metal complexes with small ligands and their structure has been elucidated through single crystal XRD. Moreover, the mode of their DNA-binding activity has been ascertained using four independent techniques which was found to be non-covalent. 2 Experimental 2.1 Materials and methods: All the solvents and reagents were of analytical grade. Distilled water was used throughout the study for synthesis and spectroscopic studies. Substituted derivatives of phenyl acetic acid were purchased from Fluka. FTIR spectra were recorded on a Nicolet-6700 FTIR spectrometer equipped with attenuated total reflectance technique in the range 4000-400 cm -1 . DNA interaction studies were performed on a Beckman U-2020 UV–Visible spectrophotometer and Ubbelohde viscometer. For spectroflourimetry, a PerkinElmer LS 45 fluorescence spectrometer with slit width of 10 nm was employed. Cyclic voltammetry was performed using SP-300 potentiostat with a typical three electrode cell. 2.2 Single crystal X-ray analyses Crystallographic data of the complexes were acquired using KAPPA APEX-II CCD diffractometer. The diffractometer was equipped with graphite monochromatic radiations Mo-Kα (λ=0.71073 Å). SAINT and multi-scan [9] were employed for data reduction and absorption corrections. Structures were solved by SHELXT-2014 [10] and refined within the WinGX package with SHELXL-2019/2 [11]. Moreover, dimethylsulfoxide (DMSO) was disordered over three positions with occupancy ratio 0.786(4): 0.132(4): 0.082(4) while the nitro-groups were disordered over two positions. The disorder was solved by using various restraints. The thermal parameters of the atoms in both parts of the disordered nitro-groups were made equal to each other by using “EADP” restraint. The nitro-groups were made flat by using “FLAT” restraint. For stabilization of the disordered parts of DMSO, thermal parameters of part 1 are made equal to each other. Similar procedure was done for other disordered parts of DMSO. DFIX and DANG restraints were used for making bond lengths and bond angles of the disordered parts in a usually acceptable range. 2.3 Experimental protocols of DNA interaction studies For absorption spectroscopy, concentrations of the complexes were optimized at 10 mM and absorbance of the pure complex solutions were taken in DMSO:water system (4:1) and then in the presence of 10, 20, 30, 40, 50, 60, 70 and 80 µM DNA. For cyclic voltammetry, the compounds were dissolved in DMSO at 4.5 mM and KCl was added as electrolyte. Voltammograms of these sample solutions were recorded in pure form and then in the presence of 15, 25, 35, 45, 55, 65, 75 and 85 µM DNA. For DNA-binding study through spectrofluorimetry, complex and ethidium bromide mixture (1:1) at 10 -6 M each was prepared in phosphate buffer (pH=7.2). Emission spectra of the mixture were taken in pure form and in the presence of 10, 20, 30, 40, 50, 60, 70 and 80 µM DNA. DNA-binding study through viscometry was performed by running the aqueous DNA solution (5 × 10 -5 M) in the Ubbelohde visometer and the time was noted by stopwatch. Then 10, 20, 30, 40, 50 and 60 µL solutions (5 × 10 -3 M) of each of the complexes was added to the same volume of DNA solution and its time of running in viscometer was noted each time. The relative viscosity was calculated from the difference in time of running. 2.4 Antioxidant activity . Different concentrations of the complexes were reacted with a fixed concentration of 2,2-diphenyl-1-picryl-hydrazil (DPPH) radical in ethanol. The samples were incubated for 30 minutes at 25 o C and spectrophotometric data were taken at 517 nm. Then the percent inhibition was calculated. 2.5 Antibacterial study The in vitro antibacterial activity of the synthesized complexes was ascertained using the agar well diffusion method [12] against Gram-positive (Bacillus subtilis, Micrococcus luteus and Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains. The cultured cells were added to the agar medium serving as nutrient. The thoroughly mixed mixture was then poured into a sterile petri plate. When it solidified, a sterile metallic borer was used to dig small wells in the medium. Cefixime and DMSO (which was used as solvent for the complex) were used as positive and negative controls, respectively. The inhibited region around the well was measured to calculate the percent activity of the complexes. 2.5 Molecular Docking Studies To analyse the binding interactions between compounds 1-4 and DNA, we conducted molecular docking studies using the AutoDock Vina program [13,14]. The DNA structure was obtained from the Protein Data Bank (PDB ID: 1BNA), while crystal structures of compounds 1-4 were used in these studies. The receptor preparation involved the elimination of water molecules, addition of non-polar hydrogen atoms, and assignment of partial atomic charges to the DNA fragment using MGLTools [15,16]. Partial atomic charges were also assigned to the ligand molecules. The ligands (compounds 1-4 ) were treated as flexible entities in docking, while the DNA was considered as rigid receptor. Blind docking was carried out with a grid size of 70×70×110 and a grid spacing of 0.375. The best-docked conformations and binding interactions were analysed using the Discovery Studio Visualizer [17]. 2.6 Syntheses of the complexes Complexes 1 and 2 were preparedby treating the aqueous sodium salts of ortho-methoxyphenyl acetate (0.84 g, 5 mmol) with copper sulphate (0.622 g, 2.5 mmol) and stirred for 3h at 60 o C. Then 3-bromopyridine ( 1 ) (0.24 mL, 2.5 mmol) or 3-methylpyridine ( 2 ) (0.24 mL, 2.5 mmol) was added and stirred for 3h again. The final products w ere the solid precipitates which were washed with distilled water and air dried. Purification and final crystallization from methanol yielded 1 and 2 . Recrystallization of the dried sample of 1 from DMSO yielded 3 . Recrystallization of the dried sample of an already published compound [18] by our research group yielded fine crystals of 4 . These crystals were analyzed by single crystal XRD technique. Complex 1: Green crystals; m.p. 173-175 °C; yield (60%). FT-IR (cm -1 ): 1621 ν(OCO) asym , 1421 ν(OCO) sym , ∆ν = 200, 3058 ν(Ar-H), 2972 ν(CH 2 ), 1610, 1459 Ar(C=C), 1242 ν(O-CH 3 ), 428 ν(Cu-N), 482 ν(Cu-O). Complex 2: Light green crystals; m.p. 179-180 °C; yield (68%). FT-IR (cm -1 ): 1604 ν(OCO) asym , 1415 ν(OCO) sym , ∆ν = 189, 3078 ν(Ar-H), 2956 ν(CH 2 ), 1604, 1465 νAr(C=C), 1246 ν(O-CH 3 ), 420 ν(Cu-N), 493 ν(Cu-O). Complex 3: Green crystals; m.p. 162-163 °C; yield (70%). FT-IR (cm -1 ): 1663 ν(OCO) asym , 1463 ν(OCO) sym , ∆ν = 200, 3074 ν(Ar-H), 2939 ν(CH 2 ), 1585, 1463 νAr(C=C), 1247 ν(O-CH 3 ), 503 ν(Cu-O). Complex 4: Bluish green crystals; m.p. 152-153 °C; yield (75%). FT-IR (cm -1 ): 1644 ν(OCO) asym , 1428 ν(OCO) sym , ∆ν = 216, 3040 ν(Ar-H), 2925 ν(CH 2 ), 1589, 1420 ν(C=C), 1455, 1349 ν(NO 2 ), 508 ν(Cu-O) 3 Results and discussion Four new copper complexes have been synthesized and isolated quantitatively. These have been obtained in crystallized form. These have been structurally characterized and the spectroscopic results are in harmony with structural elucidation results. Moreover, the biological relevance has been ascertained through their DNA-binding affinity (experimental and theoretical) as well as their anti-oxidant and anti-bacterial activity. 3.1 FTIR study FTIR spectroscopy of the pure samples of the complexes revealed all the peaks which were expected in the structures of the synthesized complexes. The most prominent peaks were those of the stretching vibrations of the carboxylate moiety. The asymmetric stretch of the carboxylate moieties of all the complexes were observed in the range 1621-1544 cm -1 while the symmetric stretching vibrations were in the range 1465-1428 cm -1 . The difference between the two peaks ∆ν for complexes 1 - 4 was 200, 189, 200 and 216 cm -1 , respectively. These ∆ν values were in the range (150-250 cm -1 ) typical of bridging bidentate coordination mode of the carboxylate moiety [19]. When the ∆ν values are below 150 cm -1 , it shows a chelate bidenatate coordination mode while ∆ν values above 250 cm -1 has been found to indicate monodentate or uncoordinated carboxylate moiety [19]. Thus for metal carboxylate complexes, ∆ν value can give valuable clue regarding the nature of carboxylate moiety. Aromatic C-H was observed on 3058, 3078, 3074 and 3040 cm -1 , respectively for complexes 1 - 4 . A closely lying peak was that of methylene CH 2 which was observed just below 3000 cm -1 for all the complexes. Similarly, ligand to copper bond was indicated by Cu-O bond stretching observed at 482, 493, 503 and 508 cm -1 , respectively for complexes 1 - 4 as observed for the same functionality in other structurally characterized copper(II) complexes [20,21]. The aromatic C=C bond was also indicated by its respective peaks. The FTIR spectra were in agreement to the structural data of the complexes. 3.2 Structural description Molecular structures of complexes 1 - 4 , drawn in mercury have been shown in Fig. 1 (A-D) while their crystallographic parameters have been listed in Tables 1 and 2. The complexes crystallized in triclinic crystal system with space group P-1. Each complex is dinuclear with two copper ions bonded by four carboxylate ligands in syn-syn fashion. These four Cu-O bonds around each copper ion constitute the square base of the square pyramidal geometry around each copper. The apical position of the square pyramid is formed by the oxygen atom of the DMSO molecule in complexes 1 and 2 and by the nitrogen atom of 3-methylpyridine and 3-bromopyridine in 3 and 4 , respectively. The paddlewheel complexes of copper(II) have both copper ions drawn closer enough by the four OCO bridges so that the inter-nuclear distance between the two ions is comparable to a covalent bond. However, a bond cannot be formed between the two copper ions along that axis because there is no suitably oriented orbital on each copper to overlap and form a bond along that axis. The central Cu-Cu bond in these molecules is not a genuine bond, rather a bond drawn by the software owing to the shorter distance between two copper ions. A crystallography software/program usually draws a bond between such ions owing to the short distance but that bond is not meaningful and metal ions are actually 5-coordinated square pyramidal in these complexes. The metal ion is bulging out of the square base towards the apical position in such complexes. It means that the Cu···Cu ̶ O angle is less than 90 o and the O ̶ Cu ̶ O/N apical is greater than 90 o . The Cu···Cu distance in paddlewheel complexes is sensitive to the basic strength of the carboxylate ligand. Thus varying the basic strength of the donor atoms, this distance can be increased or decreased and the properties dependent on this parameter can be tuned. Changing the carboxylate ligand from trifloroacetato (2.766(1) Å) to trimethylacetato (2.630(18) Å) the Cu···Cu distance is shortened as the basicity of the ligand is increased [22]. The corresponding Cu···Cu distances in the synthesized complexes lie in the range 2.619(5) - 2.671(13) Å. The basic strength of the carboxylate ligands is moderate so Cu···Cu separation is less than that of the trifloroacetate based complexes [22]. Table 1: Structural refinement parameters of complexes 1 - 4 . Complex 1 2 3 4 Empirical formula C 46 H 44 Cu 2 O 12 N 2 Br 2 C 42 H 58 Cu 2 O 12 N 4 C 42 H 54 Cu 2 O 15 S 3 C 42 H 50 N 4 Cu 2 O 19 S 3 Formula weight (g mol -1 ) 1103.73 938 1100.24 608.12 Temperature (K) 296 (2) 296 (2) 296(2) 296(2) Space group P -1 P -1 P -1 P -1 a (Ǻ) 10.1938(18) 10.2587(5) 10.2769(3) 8.3318(3) b (Ǻ) 11.1038(19) 11.0604(7) 10.5506(3) 9.4496(5) c (Ǻ) 11.3014(17) 11.2080(6) 13.1292(4) 16.8061(7) α (°) 86.680(6) 87.823(3) 77.156(2) 95.045(4) β(°) 66.562(6) 66.689(2) 70.7940(10) 100.412(3) γ (°) 79.318(6) 78.992(3) 69.967(2) 92.032(4) Volume (A 3 ) 1153.1(3) 1145.42(11) 1253.32(7) 1294.57(10) Z 1 1 1 2 ρ(calc.) (g cm -3 ) 1.589 1.360 1.458 1.560 Absorption coeff. (mm -1 ) 2.718 0.991 1.081 1.063 F(000) 558 492 574 630 Reflections collected 3101 3367 5419 4840 Goodness-of-fit on F 2 1.047 1.072 1.049 1.042 Final R index [I > 2σ(I)] 0.0502 0.103 0.0427 0.0791 Table 2: Selected bond lengths and angles of complexes 1 - 4 . Bond Lengths Å 1 2 3 4 Cu(1)-O(1) 1.957(3) 1.980(4) Cu(1)-O(1) 1.971(18) 1.964(3) Cu(1)-O(2) 1.967(3) 1.973(4) Cu(1)-O(2) 1.980(18) 1.958(3) Cu(1)-O(3) 1.973(3) 1.959(4) Cu(1)-O(3) 1.958(18) 1.965(4) Cu(1)-O(4) 1.966(4) 1.974(4) Cu(1)-O(4) 1.976(18) 1.965(4) Cu(1)-N(1) 2.187(3) 2.171(5) Cu(1)-O(5) 2.162(17) 2.138(3) Cu(1)-Cu(1) 2.639(9) 2.671(13) Cu(1)-Cu(1) 2.619(5) 2.639(10) Bond Angles ( o ) O(2)-Cu(1)-O(3) 89.41(12) 89.20(2) O(2)-Cu(1)-O(3) 89.37(9) 88.43(19) O(1)-Cu(1)-O(2) 168.02(11) 166.84(17) O(1)-Cu(1)-O(2) 168.79(7) 167.77(15) O(4)-Cu(1)-O(3) 168.12(11) 166.76(17) O(4)-Cu(1)-O(3) 168.66(7) 167.75(16) O(1)-Cu(1)-O(3) 90.01(12) 89.70(2) O(1)-Cu(1)-O(3) 89.62(9) 89.58(19) O(4)-Cu(1)-O(2) 88.82(12) 88.30(2) O(4)-Cu(1)-O(2) 89.50(9) 89.52(18) O(1)-Cu(1)-O(4) 89.29(12) 89.80(2) O(1)-Cu(1)-O(4) 89.31(8) 89.87(19) O(2)-Cu(1)-N(1) 98.40(12) 95.92(18) O(2)-Cu(1)-O(5) 96.34(8) 95.35(14) O(3)-Cu(1)-N(1) 96.40(12) 93.87(19) O(3)-Cu(1)-O(5) 97.57(7) 96.88(14) O(1)-Cu(1)-N(1) 93.50(12) 97.24(19) O(1)-Cu(1)-O(5) 94.86(8) 96.33(15) O(4)-Cu(1)-N(1) 95.48(12) 99.32(19) O(4)-Cu(1)-O(5) 93.76(7) 95.88(15) Supra-molecular chemistry: Since there is no O/F/N─H∙∙∙O/F/N interactions in the lattices of all the four complexes, there is no intermolecular H-bonding interactions. However, there are some C─H∙∙∙O interactions in complex 4. A further insight into these interactions was obtained by performing the Hirshfeld surface analysis. These intermolecular interactions have been indicated by bright red spots on the Hirshfeld surfaces mapped over d norm for complexes 1-4 as shown in Fig. 2 A-D. These contacts have been expanded to a neighboring molecule as well across the Hirshfeld surface as evident in these figures for each molecule. The fewer C─H∙∙∙O interactions in complex 4 have been shown in Fig. 2E as dotted lines. The contributions of H∙∙∙C, H∙∙∙N, H∙∙∙O and H∙∙∙H interactions to the overall packing of complexes 1-4 have been indicated in the 2D fingerprint plots shown in Fig. 3. Amongst H∙∙∙C, H∙∙∙N, H∙∙∙O and H∙∙∙H interactions, the highest percentage is that of H∙∙∙H linkage indicating a major contribution of the van der Waal’s forces in the crystal lattice of the complexes 1-4. A considerable contribution of H∙∙∙C interactions indicates contribution of C─H∙∙∙π interactions as well. There is very small percentage of C∙∙∙C interactions indicating small overlap of aromatic rings and less possibility of π ─π staking interactions. 3.3 Stability studies in solution form In order to ascertain whether the structure and geometry of the synthesized complexes remains intact in solution form, their solutions were subjected to absorption spectroscopic studies at various intervals. Since the absorption spectrum of a copper(II) complex is a function of geometry (octahedral, square planar, square pyramidal, trigonal bipyramidal and tetrahedral) around copper ion, the spectra for solution studies were taken in visible region of spectrum as shown in Fig. 4. These spectra show that the complexes remain unchanged for at least 24 hr in common solvents. 3.4 DNA-binding studies of the complexes DNA-binding potential of the complexes was explored using four different techniques. These are discussed below in detail one by one. UV-Visible spectrophotometry The complexes gave rise to ligand based well-defined absorption peaks in the UV-region following the Beer-Lambert’s Law. It means that reduction in concentration of the complexes will result in reduction in their absorbance value as per the Beer-Lambert’s Law. Adding incremental quantity of DNA will result the reduction in concentration of the complex owing to the complex-DNA adduct formation. This has been shown for 1 - 4 in Fig. 5, where the absorbance value of the pure complex represented by the uppermost plot has suffered proportionate diminution on DNA-addition. This indicates that each complex effectively binds with DNA majorly through intercalative mode of binding [5,6]. Since there is pronounced reduction in absorbance of each complex on addition of DNA and the wave length of complex suffers no appreciable change along the successive addition, such binding mode is called intercalative binding where the complex molecules simply insert between the DNA base pairs [5,6]. This binding mode is not unexpected because the complexes have plenty planar aromatic moieties in the structure through which these molecules get inserted into the DNA double strand. The binding ability has been quantitatively ascertained by calculating the binding constant K b using a simplified form of the Benesi-Hildebrand equation [23]. This was done by plotting the reciprocal molar concentration of DNA vs . the relative absorbance value as shown in Fig. 6 and the K b value was calculated from the slope to intercept ratio of the plot. The K b values calculated were 1.85, 2.05 and 1.88 and 1.92 × 10 4 M -1 , respectively for complexes 1 - 4 . Similar DNA binding potency was observed for other copper complexes as well [24]. DNA-binding study using viscometry The viscosity of DNA is sensitive to its strand length; longer strains have higher viscosity than shorter strands. Planar molecules are able to intercalate between base pairs of DNA double strands which will lengthen the DNA strand resulting in higher viscosity [5,6]. When the complexes 1 - 4 were added gradually to the DNA solution, the viscosity of DNA solution increased steadily as seen in the Fig. 7. This also indicated the intercalative mode of complexes with DNA. The same mode was indicated by UV-Visible spectroscopy as well. DNA-binding study using spectrofluorimetry Ethidium bromide (EtBr) is a potent intercalator into the DNA-base pairs. It has high emission intensity in DNA-bound form while in free state its emission intensity is quenched by the buffered solvent medium. If another molecule competing for intercalation into the DNA-base pairs is added to the solution containing DNA-EtBr adduct, it will compete with EtBr and will tend to replace the later [25]. If the added molecule successfully replaces the EtBr and gets inserted into the DNA strand, the emission intensity of the EtBr will be reduced since the quantity of the DNA-bound and emissive EtBr has been reduced. On successive addition of the synthesized complexes 1 - 4 to the solution containing DNA-EtBr adduct, its emission intensity was reduced on each addition. This showed that the complexes are able to compete successfully with EtBr for intercalation into the DNA base pairs as shown in Fig. 8 for complexes 1 - 4 . This technique indicated that the complexes are more potent intercalators than EtBr and that the mode of binding of the complexes with DNA is intercalation as deduced from the previous techniques. DNA-binding study using cyclic voltammetry Change in the concentration of an electro-active compound can be followed by cyclic voltammetry where the resulting current is changed with change in concentration. In this context, cyclic voltammograms of the complexes were recorded before and after adding variuos quantities of DNA. The voltammograms did suffer deminution in current on addition of DNA which indicated binding with the complexes as shown in Fig. 9. The diminution in current of the complexes on addition of DNA was used to calculate the binding constant of the complexes with DNA using plots shown in Fig. 10. The results of the four techniques on DNA-binding study are in harmony with each other. 3.5 Molecular Docking Studies The binding interactions of the compounds 1-4 with DNA were assessed through molecular docking analysis, which allowed us to examine how these complexes interact with their target. Fig. 11 shows the best-docked conformations of complexes 1 - 4 . In all instances, the ligands bind to DNA's major groove, with binding scores falling within the range of -6.5 to -7.4 kcal/mol. In all cases multiple conventional intermolecular hydrogen bonds are developed between the ligands and both strands of DNA base pairs showing a dual binding mode. The most effective among the docked complexes is compound 4 , with a docking score of -7.3 kcal/mol. It acts as four hydrogen bond acceptor through the oxygen of -OS(CH 3 ) 2 and -NO 2 groups. One hydrogen bond is formed with A:DA5 and three hydrogen bonds with B:DA17 and B:DA18 residues. It is also involved in π-donor hydrogen bonding through the phenyl ring and A:DG4 residue, π-sulphur interaction with A:DA6 and π-π T-shaped interaction with B:DA18 and DG10, indicating its strong binding affinity. Compounds 1-2 show equal binding affinity with a binding score of -6.9 kcal/mol. Compound 1 acts as two H-bond acceptor and interacts with A:DG2 and B:DC21. Further interactions of 1 with DNA include π-anion interaction with B:DT19, π-π T-shaped with B:DT20 and π-alkyl interaction with B:DG22. Compound 2 forms two conventional hydrogen bonds with A:DA6 and B:DA18, as well as a carbon-hydrogen bond with A:DT7, π-anion interaction with A:DG4, π-π T-shaped interaction with A:DC3 and B:DA17, and π-alkyl interaction with B:DT20. Compound 3 shows the least binding score of -6.5 kcal/mol and forms three hydrogen bonds with A:DC3 and B:DC21. The other binding interactions of 3 include carbon-hydrogen interactions, π-anion, π-π T-shaped, π-donor hydrogen bonds, and π-alkyl interactions. In summary, the molecular docking analysis reveals a robust binding relationship between these complexes and DNA, indicating their potential as promising anticancer agents. 3.6 Anti-oxidant activity of complexes Another activity of biological relevance is the ability of a complex to quench free radicals which are produced continuously in bio-systems. In order to ascertain this activity, the synthesized complexes have been treated with a free radical DPPH and the decrease in the concentration of DPPH indicated reaction between the two and quenching of the later. Plots in Fig. 12 show that with increase in concentration of complexes 1 - 4 , their scavenging activity also increased. The activity of each of complexes 2 and 3 was comparable to that of the ascorbic acid which was used as standard. The relative inhibition of the complexes showed that these complexes can be used to quench the free radicals as well. 3.7 Anti-bacterial studies The in vitro antibacterial activity of the synthesized complexes against three Gram-positive strains (Bacillus subtilis, Micrococcus luteus and Staphylococcus aureus) and a Gram-negative strain (Escherichia coli). The activity was measured by calculating the area of zone of inhibition by the complexes and was classified accordingly as in the literature [12]. Table 3 lists the observed activity of the complexes where the highest activity was observed for complexes 1 and 4 (zone of inhibition 20 and 21) against Micrococcus luteus and Staphylococcus aureus. However, their activity against Bacillus subtilis and Escherichia coli was low (zone of inhibition = 17 mm for both complexes). Complexes 1 and 4 exhibited good activity against the rest of the bacterial species. Only complex 2 showed significant activity against E. coli while moderate and low activities were exhibited against the rest of the species. The significant activity of complexes 1 and 2 might be due to the presence of bromo- and nitro-groups, respectively which are able to promote covalent and ionic interactions with cellular membranes and tissues of target bacteria. Anti-bacterial activity indicates potential biological relevance of the synthesized complexes. Table 3: Antibacterial data of the synthesized complexes Bacterial strain Parameter Bacillus subtilis Micrococcus luteus Staphylococcus aureus Escherichia Coli Average zone of inhibition (mm) Complex 1 17 20 20 17 Complex 2 18 17 14 19 Complex 3 16 16 14 13 Complex 4 17 21 21 17 Cefixime 27 30 32 31 Minimum Inhibitory Concentration (mg/mL) Complex 1 0.25 0.25 0.25 0.25 Complex 2 0.23 0.23 0.23 0.23 Complex 3 0.20 0.20 0.20 0.20 Complex 4 0.25 0.25 0.25 0.25 Concentration of each complex: 1 mg/mL in DMSO. Cefixime : 1 mg/mL. 4 Conclusion Four new carboxylate complexes of copper(II) ( 1-4 ) have been synthesized with substituted phenyl acetic acids and pyridine. These were characterized using UV-Visible and FTIR spectroscopy and single crystal XRD. The FTIR study showed the bands which indicated their synthesis and attachment of ligands to copper ion. The biological significance has been explored via DNA-binding and antioxidant activity studied by UV-Visible and fluorescence spectroscopy, cyclic voltammetry and viscometry. All the four techniques yielded coherent results of the activity in line with the in silico findings. This indicated facile and potent DNA-binding activity of the synthesized complexes. The complexes also exhibited excellent anti-oxidant activity against free radical DPPH and the activity was comparable to that of the ascorbic acid. A further support to the biological potency of the synthesized complexes was given by their potent activity against gram positive as well as gram negative bacterial strains. This preliminary study showed that the synthesized complexes can have excellent biological potential. Declarations Supplementary material: Crystallographic data for the complexes 1 - 4 reported in this paper have been deposited with the Cambridge Crystallographic Data Centre corresponding to CCDC #s 2068200, 2068201, 2068198 and 2068197, respectively. [Fax: +44 (1223)336 033]; e-mail: [email protected] . Conflict of interest statement: The authors claim no conflict of interest. Data Availability Statement: The data will be made available on request. References Cirri D, Pratesi A, Marzo T, Messori L (2021) Metallo therapeutics for COVID-19. Exploiting metal-based compounds for the discovery of new antiviral drugs. Expert Opin Drug Discov 16:39-46 Gürses C, Aktaş A, Balcıoğlu S, Fadhilah A, Gök Y, Ateş B (2022) Synthesis, characterization, DNA binding and anticancer activities of the imidazolidine-functionalized (NHC)Ru(II) complexes. J Mol Struct 1247: 131350 Hack J, Crabb SJ (2022) Platinum-Based Chemotherapy ‘Rechallenge’ in Advanced Non-ovarian Solid Malignancies. Clinical Oncology 34: E329-E344 Wang YR, Chen SF, Wu CC et al (2017) Producing irreversible topoisomerase II-mediated DNA breaks by site-specific Pt(II)-methionine coordination chemistry. Nucleic Acids Res 45: 10861–10871 Kolbeck PJ, Vanderlinden W, Gemmecker G et al (2021) Molecular structure, DNA binding mode, photophysical properties and recommendations for use of SYBR Gold. Nucleic Acids Res 49: 5143–5158 Berdnikova DV, Sosnin NI, Fedorova OA, Ihmels H (2017) Governing the DNA-binding mode of styryl dyes by the length of their alkyl substituents – From intercalation to major groove binding. Org Biomol Chem 16: 545-554 Iqbal M, Haleem MA, Ali S et al (2021) Centro-symmetric paddlewheel copper(II) carboxylates: Synthesis, structural description, DNA-binding and molecular docking studies. Polyhedron 208: 115407 Iqbal M, Ullah N, Haleem MA et al (2023) Synthesis, crystal structure elucidation, DNA-binding and micellization behavior of copper(II) carboxylate complexes. Results Chemistry 5: 100700 Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Sheldrick GM, (2015) SHELXT–Integrated space-group and crystal-structure determination. Acta Crystallogr. A: Foundations and Advances 71: 3-8. Sheldrick GM, (2015) Crystal structure refinement with SHELXL. Acta Cryst C 71:3–8 Iqbal M, Ali S, Tahir MN, Nawaz A, Anderson PA, Khan W, (2019) Mono- and poly-nuclear copper(II) carboxylates withflourous ligands: Synthesis, structure and improved properties, Inorg Chim Acta 498: 119177 Eberhardt J, Santos-Martins D, Tillack AF, Forli S, (2021) AutoDock Vina 1.2.0: New Docking Methods, Expanded Force Field, and Python Bindings. J Chem Inf Model 61: 3891-3898. Trott O, Olson AJ, (2010) AutoDock Vina: improving the speed and accuracy of docking with a new scoring function, efficient optimization, and multithreading. J Comput Chem 31: 455-461. Morris GM, Huey R, Lindstrom W, Sanner MF, Belew RK, Goodsell DS, Olson AJ, (2009) AutoDock4 and AutoDockTools4: Automated docking with selective receptor flexibility. J Comput Chem 30: 2785-2791. Sanner MF, (1999) Python: a programming language for software integration and development. J. Mol. Graph. Model. 17: 57-61. Accelrys S, Discovery studio modeling environment. Dassault Systèmes BIOVIA: San Diego, CA, USA 2017. Mushtaq A, Ali S, Iqbal M, Tahir MN, Ismail H (2017) Synthesis of a New Heteroleptic Copper(II) Complex: Structural Elucidation, DNA Binding and In-vitroAlpha Glucosidase Inhibition Studies. J Chem Soc Pak 39: 471-477 Iqbal M, Ahmad A, Ali S et al (2013) Dimeric ‘‘paddle-wheel’’ carboxylates of copper(II): Synthesis, crystal structure and electrochemical studies. Polyhedron 50: 524–531 Dakua VK et al., (2023) Synthesis, crystal structure, Hirshfeld surface, and DFT studies of a Copper(II) complex of 5,5′-dimethyl-2,2′-bipyridine and 1,2,2-trimethylcyclopentane-1,3-dicarboxylic acid, Results Chem 6: 101050. Hussain A, AlAjmi MF, Rehman MT et al., (2019) Copper(II) complexes as potential anticancer and Nonsteroidal anti-inflammatory agents: In vitro and in vivo studies, Sci Rep 9: 5237 Iqbal M, Ali S, Muhammad N, Sohail M (2013) Synthesis, crystal structures and electrochemical characterization of dinuclear paddlewheel copper(II) carboxylates. Polyhedron 57: 83–93 Benesi HA, Hildebrand JH (1949) A Spectrophotometric Investigation of the Interaction of Iodine with Aromatic Hydrocarbons. J Am Chem Soc 71: 2703–2707 Sureshbabu P, Varghese B, Sujitha E, Sabiah S (2022) Syntheses, structure, DNA docking and antimicrobial studies of copper(II) complexes with diethylenetriamine and N-bidentate ligands. Inorg Chim Acta 536: article No. 120898 Phadte AA, Banerjee S, Mate NA, Banerjee A (2019) Spectroscopic and viscometric determination of DNA-binding modes of some bioactive dibenzodioxins and phenazines, Biochem Biophys Rep 18: article No. 100629 Scheme Scheme 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Scheme1.png Scheme 1: synthesis of complexes 1 and 2. TheIndexAbstract.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 08 Mar, 2024 Submission checks completed at journal 22 Feb, 2024 Editor assigned by journal 22 Feb, 2024 First submitted to journal 16 Feb, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3960580","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":274308847,"identity":"542d65a2-e5dd-410c-9cc6-94b925b39c9c","order_by":0,"name":"Afifa Mushtaq","email":"","orcid":"","institution":"Quaid-i-Azam University","correspondingAuthor":false,"prefix":"","firstName":"Afifa","middleName":"","lastName":"Mushtaq","suffix":""},{"id":274308848,"identity":"d7fd7881-ce2d-475f-ad62-5969e8d5b13e","order_by":1,"name":"Muhammad 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07:15:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3960580/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3960580/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":51661688,"identity":"2691390d-9697-4827-be56-9b366a597125","added_by":"auto","created_at":"2024-02-26 19:35:56","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":568188,"visible":true,"origin":"","legend":"\u003cp\u003eMolecular structures of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4 \u003c/strong\u003e(A-D) drawn in mercury.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/6565e8e35c54b475a7d255e0.jpg"},{"id":51661683,"identity":"c6c08be6-7b67-408e-9c9b-4e1a19ee0ece","added_by":"auto","created_at":"2024-02-26 19:35:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":698350,"visible":true,"origin":"","legend":"\u003cp\u003eHirshfeld surfaces of the synthesized complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4 \u003c/strong\u003e(A-D) mapped over \u003cem\u003ed\u003c/em\u003e\u003csub\u003enorm\u003c/sub\u003e showing intermolecular interactions indicated as dotted lines and the C─H∙∙∙O interactions in complex 4 (E).\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/2971dee1dfd0bde6d0255142.jpg"},{"id":51661678,"identity":"3122103a-386e-4cec-a73d-28f3b5ffc125","added_by":"auto","created_at":"2024-02-26 19:35:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":936122,"visible":true,"origin":"","legend":"\u003cp\u003eTwo-dimensional fingerprint plots showing the percent contribution of H∙∙∙C, H∙∙∙N, H∙∙∙O and H∙∙∙H interactions to the overall packing of complexes 1-4 (A-D)\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/126e5f744e033213f8be2098.jpg"},{"id":51661665,"identity":"f6bd6c96-616f-4a1c-bd93-f30e21c4f9cf","added_by":"auto","created_at":"2024-02-26 19:35:55","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":289360,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorption spectra of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4 \u003c/strong\u003eat various time intervals.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/823ed2b78911a0b4e52d6e0a.jpg"},{"id":51661685,"identity":"effce0c1-fda6-4298-b4a0-ed9effd6cc7d","added_by":"auto","created_at":"2024-02-26 19:35:56","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":353194,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorbance spectra of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4 \u003c/strong\u003ein the absence of DNA (upper most peak designated as a) and presence of 10, 20, 30, 40, 50, 60, 70 and 80 µM DNA (designated as b-i) showing decrease in absorbance with the addition of DNA.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/707b1533a4fa67b17f7f8edb.jpg"},{"id":51661658,"identity":"5e98f068-ab31-4942-be09-e0afc9bc9d78","added_by":"auto","created_at":"2024-02-26 19:35:53","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":166600,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of 1/[DNA] vs. A\u003csub\u003eo\u003c/sub\u003e/(A-A\u003csub\u003eo\u003c/sub\u003e) for the calculation of the binding constants of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/fb03bbfc503a5e8ccada2115.jpg"},{"id":51661662,"identity":"23eb1408-f3f1-4640-8d9b-479e2d2d03b6","added_by":"auto","created_at":"2024-02-26 19:35:54","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":211924,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of the ratio of molar concentrations of complex/DNA \u003cem\u003evs\u003c/em\u003e. relative viscosity for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/8aa985ddab79fbf7881f471b.jpg"},{"id":51661655,"identity":"31d00aaf-1d4d-4ac8-bced-8ae7429f8f9d","added_by":"auto","created_at":"2024-02-26 19:35:50","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":521332,"visible":true,"origin":"","legend":"\u003cp\u003eChange in florescence intensity of ethidium bromide on addition of complex to the solution containing DNA-EtBr adduct. A-D correspond to complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/4339216db39f1fb648cfaf09.jpg"},{"id":51661690,"identity":"2dd5e389-fd7f-4c88-a826-cab0273aa804","added_by":"auto","created_at":"2024-02-26 19:35:57","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":404868,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltamograms of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4 (A-D)\u003c/strong\u003e in the absence of DNA (upper most voltamogram designated as a) and presence of 15, 25, 35 and 45 µM DNA (designated as b-e) showing decrease in absorbance with the addition of DNA.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/cd3037d57d82a8a638d2bad6.jpg"},{"id":51661661,"identity":"db29a8e4-028e-4ef7-8ae6-2cde73454bbc","added_by":"auto","created_at":"2024-02-26 19:35:54","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":163339,"visible":true,"origin":"","legend":"\u003cp\u003ePlots of the log. of current \u003cem\u003evs \u003c/em\u003elog. of 1/DNA of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/e83fbde6fa798edf1a82f6a8.jpg"},{"id":51661765,"identity":"25892e7c-5727-42fd-b3ad-8ac24b728d92","added_by":"auto","created_at":"2024-02-26 19:43:56","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":937922,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical illustration of binding between compounds \u003cstrong\u003e1-4 \u003c/strong\u003eand DNA. Adjustment of compounds \u003cstrong\u003e1-4 \u003c/strong\u003ein the major groove of DNA, (left panel), 3D view of the interactions between compounds \u003cstrong\u003e1-4\u003c/strong\u003e and DNA-base pairs (middle panel) and 2D illustration of various interactions between compounds \u003cstrong\u003e1-4\u003c/strong\u003e at the binding site.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/58b80e1dbc2f20ce9bb3c22f.jpg"},{"id":51661674,"identity":"95a9be32-600d-4e87-af05-deb43f8bab12","added_by":"auto","created_at":"2024-02-26 19:35:55","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":296881,"visible":true,"origin":"","legend":"\u003cp\u003eDPPH radical scavenging activity of complexes \u003cstrong\u003e1-4\u003c/strong\u003e relative to ascorbic acid.\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/b84a0dc9081fa2c2cd28e38b.jpg"},{"id":51661766,"identity":"7c8daf57-32c2-43dc-b4be-52a76169c379","added_by":"auto","created_at":"2024-02-26 19:44:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1879283,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/e7f09309-fe60-4123-9c05-d5ae7b5793e8.pdf"},{"id":51661670,"identity":"283038d6-4fad-478c-8073-dea8b876b15e","added_by":"auto","created_at":"2024-02-26 19:35:55","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":23316,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 1: synthesis of complexes 1 and 2.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/07a6ab60d5d537aaf3395861.png"},{"id":51661680,"identity":"4ccfc843-99bd-4c98-a826-ff1b8de95d6a","added_by":"auto","created_at":"2024-02-26 19:35:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":97467,"visible":true,"origin":"","legend":"","description":"","filename":"TheIndexAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-3960580/v1/70cbc064a744b54cc853f896.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synthesis, structural elucidation, DNA-binding and anti-oxidant activities of centrosymmetric paddlewheel copper carboxylate complexes","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe continuing importance of metallo-pharmaceuticals in synthetic chemistry research groups is hopeful and necessary for making new advances in the field [1]. Among various parameters used for testing the biological importance of the newly synthesized complexes/drugs is their interaction with DNA. This activity has long been intensely investigated in the pursuit to develop new functional materials for uses in medicine and biotechnology [2]. The DNA-binding activity of the complexes is important since such substances can ultimately develop into agents which will stop the uncontrolled cell division in the tumorous tissues.\u003c/p\u003e\n\u003cp\u003eSeveral types of compounds are being under investigation to be developed into efficient DNA-binding/cleaving agents. The metal based DNA-binding agents have developmental history dating back to cis-platin which is still the currently used anti-tumor drug, despite numerous well established side effects [3]. The metal based drugs would be hopeful in performing the dual function of interacting with DNA electrostatically through metal ion as well as through the attached ligand moieties. However, since platinum based drugs bind with DNA irreversibly, it has been proposed that the large side effects arising from these drugs might be due to their binding mode. The toxicity has also been attributed to the intrinsic toxicity of the precious platinum metal [3,4]. Therefore, it has been proposed that the preferable binding mode of the drugs with DNA should be non-covalent and reversible type.\u003c/p\u003e\n\u003cp\u003eThe non-covalent binding mode has been classified as electrostatic, groove and intercalative binding modes. Keeping in view these points, it is sought that the metal as well as the ligands selected for the synthesis of compounds destined for DNA-binding activity must be non-toxic and harmless to the normal tissues. Additionally, the mode of interaction of the prepared compounds must be preferably non-covalent and reversible [5,6]. In this context, a bio-essential metal will be most preferable with biologically benign ligands. In this context, various substitution derivatives of phenyl acetate have been used as ligands for the synthesis of these complexes which have several preferable features such as small size, water solubility, intermediate Lewis base strength, variable coordinating ability to metal ion. The resulting complexes are expected to have size suitable to permeate easily through biological membranes. The inorganic groups such as nitro and bromo-groups on these ligands promote electrostatic interactions with biological molecules such as DNA. In continuation of our previous work [7,8] we have synthesized copper metal complexes with small ligands and their structure has been elucidated through single crystal XRD. Moreover, the mode of their DNA-binding activity has been ascertained using four independent techniques which was found to be non-covalent.\u003c/p\u003e"},{"header":"2 Experimental ","content":"\u003cp\u003e\u003cstrong\u003e2.1 Materials and methods:\u003c/strong\u003e All the solvents and reagents were of analytical grade. Distilled water was used throughout the study for synthesis and spectroscopic studies. Substituted derivatives of phenyl acetic acid were purchased from Fluka. FTIR spectra were recorded on a Nicolet-6700 FTIR spectrometer equipped with attenuated total reflectance technique in the range 4000-400 cm\u003csup\u003e-1\u003c/sup\u003e. DNA interaction studies were performed on a Beckman U-2020 UV\u0026ndash;Visible spectrophotometer and Ubbelohde viscometer. For spectroflourimetry, a PerkinElmer LS 45 fluorescence spectrometer with slit width of 10 nm was employed. Cyclic voltammetry was performed using SP-300 potentiostat with a typical three electrode cell.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Single crystal X-ray analyses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCrystallographic data of the complexes were acquired using KAPPA APEX-II CCD diffractometer. The diffractometer was equipped with graphite monochromatic radiations Mo-K\u0026alpha; (\u0026lambda;=0.71073 \u0026Aring;). SAINT and multi-scan [9] were employed for data reduction and absorption corrections. Structures were solved by SHELXT-2014 [10] and refined within the WinGX package with SHELXL-2019/2 [11]. \u003c/p\u003e\n\u003cp\u003eMoreover, dimethylsulfoxide (DMSO) was disordered over three positions with occupancy ratio 0.786(4): 0.132(4): 0.082(4) while the nitro-groups were disordered over two positions. The disorder was solved by using various restraints. The thermal parameters of the atoms in both parts of the disordered nitro-groups were made equal to each other by using \u0026ldquo;EADP\u0026rdquo; restraint. The nitro-groups were made flat by using \u0026ldquo;FLAT\u0026rdquo; restraint. For stabilization of the disordered parts of DMSO, thermal parameters of part 1 are made equal to each other. Similar procedure was done for other disordered parts of DMSO. DFIX and DANG restraints were used for making bond lengths and bond angles of the disordered parts in a usually acceptable range.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Experimental protocols of DNA interaction studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor absorption spectroscopy, concentrations of the complexes were optimized at 10 mM and absorbance of the pure complex solutions were taken in DMSO:water system (4:1) and then in the presence of 10, 20, 30, 40, 50, 60, 70 and 80 \u0026micro;M DNA. \u003c/p\u003e\n\u003cp\u003eFor cyclic voltammetry, the compounds were dissolved in DMSO at 4.5 mM and KCl was added as electrolyte. Voltammograms of these sample solutions were recorded in pure form and then in the presence of 15, 25, 35, 45, 55, 65, 75 and 85 \u0026micro;M DNA. \u003c/p\u003e\n\u003cp\u003eFor DNA-binding study through spectrofluorimetry, complex and ethidium bromide mixture (1:1) at 10\u003csup\u003e-6\u003c/sup\u003e M each was prepared in phosphate buffer (pH=7.2). Emission spectra of the mixture were taken in pure form and in the presence of 10, 20, 30, 40, 50, 60, 70 and 80 \u0026micro;M DNA.\u003c/p\u003e\n\u003cp\u003eDNA-binding study through viscometry was performed by running the aqueous DNA solution (5 \u0026times; 10\u003csup\u003e-5\u003c/sup\u003e M) in the Ubbelohde visometer and the time was noted by stopwatch. Then 10, 20, 30, 40, 50 and 60 \u0026micro;L solutions (5 \u0026times; 10\u003csup\u003e-3\u003c/sup\u003e M) of each of the complexes was added to the same volume of DNA solution and its time of running in viscometer was noted each time. The relative viscosity was calculated from the difference in time of running. \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Antioxidant activity\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eDifferent concentrations of the complexes were reacted with a fixed concentration of 2,2-diphenyl-1-picryl-hydrazil (DPPH) radical in ethanol. The samples were incubated for 30 minutes at 25 \u003csup\u003eo\u003c/sup\u003eC and spectrophotometric data were taken at 517 nm. Then the percent inhibition was calculated. \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5 Antibacterial study\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe in vitro antibacterial activity of the synthesized complexes was ascertained using the agar well diffusion method [12] against Gram-positive (Bacillus subtilis, Micrococcus luteus and Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains. The cultured cells were added to the agar medium serving as nutrient. The thoroughly mixed mixture was then poured into a sterile petri plate. When it solidified, a sterile metallic borer was used to dig small wells in the medium. Cefixime and DMSO (which was used as solvent for the complex) were used as positive and negative controls, respectively. The inhibited region around the well was measured to calculate the percent activity of the complexes. \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5\u003c/strong\u003e\u003cstrong\u003e Molecular Docking Studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo analyse the binding interactions between compounds \u003cstrong\u003e1-4\u003c/strong\u003e and DNA, we conducted molecular docking studies using the AutoDock Vina program [13,14]. The DNA structure was obtained from the Protein Data Bank (PDB ID: 1BNA), while crystal structures of compounds \u003cstrong\u003e1-4\u003c/strong\u003e were used in these studies. The receptor preparation involved the elimination of water molecules, addition of non-polar hydrogen atoms, and assignment of partial atomic charges to the DNA fragment using MGLTools [15,16]. Partial atomic charges were also assigned to the ligand molecules. The ligands (compounds \u003cstrong\u003e1-4\u003c/strong\u003e) were treated as flexible entities in docking, while the DNA was considered as rigid receptor. Blind docking was carried out with a grid size of 70\u0026times;70\u0026times;110 and a grid spacing of 0.375. The best-docked conformations and binding interactions were analysed using the Discovery Studio Visualizer [17].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.6 Syntheses of the complexes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eComplexes \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e2 \u003c/strong\u003ewere preparedby treating the aqueous sodium salts of ortho-methoxyphenyl acetate (0.84 g, 5 mmol) with copper sulphate (0.622 g, 2.5 mmol) and stirred for 3h at 60 \u003csup\u003eo\u003c/sup\u003eC. Then 3-bromopyridine (\u003cstrong\u003e1\u003c/strong\u003e) (0.24 mL, 2.5 mmol) or 3-methylpyridine (\u003cstrong\u003e2\u003c/strong\u003e) (0.24 mL, 2.5 mmol) was added and stirred for 3h again. The final products w ere the solid precipitates which were washed with distilled water and air dried. Purification and final crystallization from methanol yielded \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e2\u003c/strong\u003e. Recrystallization of the dried sample of \u003cstrong\u003e1\u003c/strong\u003e from DMSO yielded \u003cstrong\u003e3\u003c/strong\u003e. Recrystallization of the dried sample of an already published compound [18] by our research group yielded fine crystals of \u003cstrong\u003e4\u003c/strong\u003e. These crystals were analyzed by single crystal XRD technique.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComplex 1:\u003c/strong\u003e Green crystals; m.p. 173-175 \u0026deg;C; yield (60%). FT-IR (cm\u003csup\u003e-1\u003c/sup\u003e): 1621 \u0026nu;(OCO)\u003csub\u003easym\u003c/sub\u003e, 1421 \u0026nu;(OCO)\u003csub\u003esym\u003c/sub\u003e, ∆\u0026nu; = 200, 3058 \u0026nu;(Ar-H), 2972 \u0026nu;(CH\u003csub\u003e2\u003c/sub\u003e), 1610, 1459 Ar(C=C), 1242 \u0026nu;(O-CH\u003csub\u003e3\u003c/sub\u003e), 428 \u0026nu;(Cu-N), 482 \u0026nu;(Cu-O).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComplex 2:\u003c/strong\u003e Light green crystals; m.p. 179-180 \u0026deg;C; yield (68%). FT-IR (cm\u003csup\u003e-1\u003c/sup\u003e): 1604 \u0026nu;(OCO)\u003csub\u003easym\u003c/sub\u003e, 1415 \u0026nu;(OCO)\u003csub\u003esym\u003c/sub\u003e, ∆\u0026nu; = 189, 3078 \u0026nu;(Ar-H), 2956 \u0026nu;(CH\u003csub\u003e2\u003c/sub\u003e), 1604, 1465 \u0026nu;Ar(C=C), 1246 \u0026nu;(O-CH\u003csub\u003e3\u003c/sub\u003e), 420 \u0026nu;(Cu-N), 493 \u0026nu;(Cu-O).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComplex 3:\u003c/strong\u003e Green crystals; m.p. 162-163 \u0026deg;C; yield (70%). FT-IR (cm\u003csup\u003e-1\u003c/sup\u003e): 1663 \u0026nu;(OCO)\u003csub\u003easym\u003c/sub\u003e, 1463 \u0026nu;(OCO)\u003csub\u003esym\u003c/sub\u003e, ∆\u0026nu; = 200, 3074 \u0026nu;(Ar-H), 2939 \u0026nu;(CH\u003csub\u003e2\u003c/sub\u003e), 1585, 1463 \u0026nu;Ar(C=C), 1247 \u0026nu;(O-CH\u003csub\u003e3\u003c/sub\u003e), 503 \u0026nu;(Cu-O).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComplex 4:\u003c/strong\u003e Bluish green crystals; m.p. 152-153 \u0026deg;C; yield (75%). FT-IR (cm\u003csup\u003e-1\u003c/sup\u003e): 1644 \u0026nu;(OCO)\u003csub\u003easym\u003c/sub\u003e, 1428 \u0026nu;(OCO)\u003csub\u003esym\u003c/sub\u003e, ∆\u0026nu; = 216, 3040 \u0026nu;(Ar-H), 2925 \u0026nu;(CH\u003csub\u003e2\u003c/sub\u003e), 1589, 1420 \u0026nu;(C=C), 1455, 1349 \u0026nu;(NO\u003csub\u003e2\u003c/sub\u003e), 508 \u0026nu;(Cu-O)\u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003cp\u003eFour new copper complexes have been synthesized and isolated quantitatively. These have been obtained in crystallized form. These have been structurally characterized and the spectroscopic results are in harmony with structural elucidation results. Moreover, the biological relevance has been ascertained through their DNA-binding affinity (experimental and theoretical) as well as their anti-oxidant and anti-bacterial activity.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1 FTIR study\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFTIR spectroscopy of the pure samples of the complexes revealed all the peaks which were expected in the structures of the synthesized complexes. The most prominent peaks were those of the stretching vibrations of the carboxylate moiety. The asymmetric stretch of the carboxylate moieties of all the complexes were observed in the range 1621-1544 cm\u003csup\u003e-1\u003c/sup\u003e while the symmetric stretching vibrations were in the range 1465-1428 cm\u003csup\u003e-1\u003c/sup\u003e. The difference between the two peaks ∆\u0026nu; for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e was 200, 189, 200 and 216 cm\u003csup\u003e-1\u003c/sup\u003e, respectively. These ∆\u0026nu; values were in the range (150-250 cm\u003csup\u003e-1\u003c/sup\u003e) typical of bridging bidentate coordination mode of the carboxylate moiety [19]. When the ∆\u0026nu; values are below 150 cm\u003csup\u003e-1\u003c/sup\u003e, it shows a chelate bidenatate coordination mode while ∆\u0026nu; values above 250 cm\u003csup\u003e-1\u003c/sup\u003e has been found to indicate monodentate or uncoordinated carboxylate moiety [19]. Thus for metal carboxylate complexes, ∆\u0026nu; value can give valuable clue regarding the nature of carboxylate moiety.\u003c/p\u003e\n\u003cp\u003eAromatic C-H was observed on 3058, 3078, 3074 and 3040 cm\u003csup\u003e-1\u003c/sup\u003e, respectively for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e. A closely lying peak was that of methylene CH\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ewhich was observed just below 3000 cm\u003csup\u003e-1\u003c/sup\u003e for all the complexes. Similarly, ligand to copper bond was indicated by Cu-O bond stretching observed at 482, 493, 503 and 508 cm\u003csup\u003e-1\u003c/sup\u003e, respectively for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u0026nbsp;\u003c/strong\u003eas observed for the same functionality in other structurally characterized copper(II) complexes [20,21]. The aromatic C=C bond was also indicated by its respective peaks. The FTIR spectra were in agreement to the structural data of the complexes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Structural description\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMolecular structures of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e, drawn in mercury have been shown in Fig. 1 (A-D) while their crystallographic parameters have been listed in Tables 1 and 2. The complexes crystallized in triclinic crystal system with space group P-1. Each complex is dinuclear with two copper ions bonded by four carboxylate ligands in \u003cem\u003esyn-syn\u003c/em\u003e fashion. These four Cu-O bonds around each copper ion constitute the square base of the square pyramidal geometry around each copper. The apical position of the square pyramid is formed by the oxygen atom of the DMSO molecule in complexes \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e2\u003c/strong\u003e and by the nitrogen atom of 3-methylpyridine and 3-bromopyridine in \u003cstrong\u003e3\u003c/strong\u003e and \u003cstrong\u003e4\u003c/strong\u003e, respectively.\u003c/p\u003e\n\u003cp\u003eThe paddlewheel complexes of copper(II) have both copper ions drawn closer enough by the four OCO bridges so that the inter-nuclear distance between the two ions is comparable to a covalent bond. However, a bond cannot be formed between the two copper ions along that axis because there is no suitably oriented orbital on each copper to overlap and form a bond along that axis. The central Cu-Cu bond in these molecules is not a genuine bond, rather a bond drawn by the software owing to the shorter distance between two copper ions. A crystallography software/program usually draws a bond between such ions owing to the short distance but that bond is not meaningful and metal ions are actually 5-coordinated square pyramidal in these complexes.\u003c/p\u003e\n\u003cp\u003eThe metal ion is bulging out of the square base towards the apical position in such complexes. It means that the Cu\u0026middot;\u0026middot;\u0026middot;Cu ̶ O angle is less than 90\u003csup\u003eo\u003c/sup\u003e and the O ̶ Cu ̶ O/N\u003csub\u003eapical\u003c/sub\u003e is greater than 90\u003csup\u003eo\u003c/sup\u003e. The Cu\u0026middot;\u0026middot;\u0026middot;Cu distance in paddlewheel complexes is sensitive to the basic strength of the carboxylate ligand. Thus varying the basic strength of the donor atoms, this distance can be increased or decreased and the properties dependent on this parameter can be tuned. Changing the carboxylate ligand from trifloroacetato (2.766(1) Å) to trimethylacetato (2.630(18) Å) the Cu\u0026middot;\u0026middot;\u0026middot;Cu distance is shortened as the basicity of the ligand is increased [22]. The corresponding Cu\u0026middot;\u0026middot;\u0026middot;Cu distances in the synthesized complexes lie in the range 2.619(5) - 2.671(13) Å. The basic strength of the carboxylate ligands is moderate so Cu\u0026middot;\u0026middot;\u0026middot;Cu separation is less than that of the trifloroacetate based complexes [22].\u003c/p\u003e\n\u003cp\u003eTable 1: Structural refinement parameters of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eComplex\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEmpirical formula\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eC\u003csub\u003e46\u003c/sub\u003eH\u003csub\u003e44\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eC\u003csub\u003e42\u003c/sub\u003eH\u003csub\u003e58\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eC\u003csub\u003e42\u003c/sub\u003eH\u003csub\u003e54\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e15\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eC\u003csub\u003e42\u003c/sub\u003eH\u003csub\u003e50\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e19\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eFormula weight (g mol\u003csup\u003e-1\u003c/sup\u003e)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1103.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e938\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1100.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e608.12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTemperature (K)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e296 (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e296 (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e296(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e296(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSpace group\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eP -1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eP -1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eP -1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eP -1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ea (Ǻ)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10.1938(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10.2587(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10.2769(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e8.3318(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eb (Ǻ)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e11.1038(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e11.0604(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10.5506(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e9.4496(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ec (Ǻ)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e11.3014(17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e11.2080(6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e13.1292(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e16.8061(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha; (\u0026deg;)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e86.680(6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e87.823(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e77.156(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e95.045(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026beta;(\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e66.562(6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e66.689(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e70.7940(10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e100.412(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026gamma; (\u0026deg;)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e79.318(6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e78.992(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e69.967(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e92.032(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eVolume (A\u003csup\u003e3\u003c/sup\u003e)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1153.1(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1145.42(11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1253.32(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1294.57(10)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eZ\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026rho;(calc.) (g cm\u003csup\u003e-3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.589\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.360\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.458\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.560\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAbsorption coeff. (mm\u003csup\u003e-1\u003c/sup\u003e)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.718\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.991\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.081\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.063\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF(000)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e558\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e492\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e574\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e630\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eReflections collected\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3101\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3367\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e5419\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4840\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eGoodness-of-fit on F\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.047\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.072\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.049\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.042\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eFinal R index [I \u0026gt; 2\u0026sigma;(I)]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.0502\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.0427\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.0791\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 2: Selected bond lengths and angles of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\"\u003e\n \u003cp\u003eBond Lengths \u0026Aring;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.957(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.980(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.971(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.964(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.967(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.973(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.980(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.958(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.973(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.959(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.958(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.965(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(4)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.966(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.974(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(4)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.976(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.965(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-N(1)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.187(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.171(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-O(5)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.162(17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.138(3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-Cu(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.639(9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.671(13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCu(1)-Cu(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.619(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.639(10)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\"\u003e\n \u003cp\u003eBond Angles (\u003csup\u003eo\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(2)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.41(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.20(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(2)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.37(9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e88.43(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e168.02(11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e166.84(17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e168.79(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e167.77(15)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e168.12(11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e166.76(17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e168.66(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e167.75(16)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e90.01(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.70(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.62(9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.58(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e88.82(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e88.30(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-O(2)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.50(9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.52(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.29(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.80(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.31(8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e89.87(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(2)-Cu(1)-N(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e98.40(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e95.92(18)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(2)-Cu(1)-O(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e96.34(8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e95.35(14)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(3)-Cu(1)-N(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e96.40(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e93.87(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(3)-Cu(1)-O(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e97.57(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e96.88(14)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-N(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e93.50(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e97.24(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(1)-Cu(1)-O(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e94.86(8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e96.33(15)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-N(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e95.48(12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e99.32(19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eO(4)-Cu(1)-O(5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e93.76(7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e95.88(15)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eSupra-molecular chemistry:\u0026nbsp;\u003c/strong\u003eSince there is no O/F/N─H∙∙∙O/F/N interactions in the lattices of all the four complexes, there is no intermolecular H-bonding interactions. However, there are some C─H∙∙∙O interactions in complex 4. A further insight into these interactions was obtained by performing the Hirshfeld surface analysis. These intermolecular interactions have been indicated by bright red spots on the Hirshfeld surfaces mapped over\u003cem\u003e\u0026nbsp;d\u003c/em\u003e\u003csub\u003enorm\u0026nbsp;\u003c/sub\u003efor complexes 1-4 as shown in Fig. 2 A-D. These contacts have been expanded to a neighboring molecule as well across the Hirshfeld surface as evident in these figures for each molecule. The fewer C─H∙∙∙O interactions in complex 4 have been shown in Fig. 2E as dotted lines.\u003c/p\u003e\n\u003cp\u003eThe contributions of H∙∙∙C, H∙∙∙N, H∙∙∙O and H∙∙∙H interactions to the overall packing of complexes 1-4 have been indicated in the 2D fingerprint plots shown in Fig. 3. Amongst H∙∙∙C, H∙∙∙N, H∙∙∙O and H∙∙∙H interactions, the highest percentage is that of H∙∙∙H linkage indicating a major contribution of the van der Waal\u0026rsquo;s forces in the crystal lattice of the complexes 1-4. A considerable contribution of H∙∙∙C interactions indicates contribution of C─H∙∙∙\u0026pi; interactions as well. There is very small percentage of C∙∙∙C interactions indicating small overlap of aromatic rings and less possibility of \u0026pi; ─\u0026pi; staking interactions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Stability studies in solution form\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn order to ascertain whether the structure and geometry of the synthesized complexes remains intact in solution form, their solutions were subjected to absorption spectroscopic studies at various intervals. Since the absorption spectrum of a copper(II) complex is a function of geometry (octahedral, square planar, square pyramidal, trigonal bipyramidal and tetrahedral) around copper ion, the spectra for solution studies were taken in visible region of spectrum as shown in Fig. 4. These spectra show that the complexes remain unchanged for at least 24 hr in common solvents.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4 DNA-binding studies of the complexes\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDNA-binding potential of the complexes was explored using four different techniques. These are discussed below in detail one by one.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUV-Visible spectrophotometry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe complexes gave rise to ligand based well-defined absorption peaks in the UV-region following the Beer-Lambert\u0026rsquo;s Law. It means that reduction in concentration of the complexes will result in reduction in their absorbance value as per the Beer-Lambert\u0026rsquo;s Law. Adding incremental quantity of DNA will result the reduction in concentration of the complex owing to the complex-DNA adduct formation. This has been shown for \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u0026nbsp;\u003c/strong\u003ein Fig. 5, where the absorbance value of the pure complex represented by the uppermost plot has suffered proportionate diminution on DNA-addition. This indicates that each complex effectively binds with DNA majorly through intercalative mode of binding [5,6]. Since there is pronounced reduction in absorbance of each complex on addition of DNA and the wave length of complex suffers no appreciable change along the successive addition, such binding mode is called intercalative binding where the complex molecules simply insert between the DNA base pairs [5,6]. This binding mode is not unexpected because the complexes have plenty planar aromatic moieties in the structure through which these molecules get inserted into the DNA double strand. The binding ability has been quantitatively ascertained by calculating the binding constant K\u003csub\u003eb\u003c/sub\u003e using a simplified form of the Benesi-Hildebrand equation [23]. This was done by plotting the reciprocal molar concentration of DNA \u003cem\u003evs\u003c/em\u003e. the relative absorbance value as shown in Fig. 6 and the K\u003csub\u003eb\u003c/sub\u003e value was calculated from the slope to intercept ratio of the plot. The K\u003csub\u003eb\u003c/sub\u003e values calculated were 1.85, 2.05 and 1.88 and 1.92 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e M\u003csup\u003e-1\u003c/sup\u003e, respectively for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e. Similar DNA binding potency was observed for other copper complexes as well [24].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDNA-binding study using viscometry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe viscosity of DNA is sensitive to its strand length; longer strains have higher viscosity than shorter strands. Planar molecules are able to intercalate between base pairs of DNA double strands which will lengthen the DNA strand resulting in higher viscosity [5,6]. When the complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u0026nbsp;\u003c/strong\u003ewere added gradually to the DNA solution, the viscosity of DNA solution increased steadily as seen in the Fig. 7. This also indicated the intercalative mode of complexes with DNA. The same mode was indicated by UV-Visible spectroscopy as well.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDNA-binding study using spectrofluorimetry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthidium bromide (EtBr) is a potent intercalator into the DNA-base pairs. It has high emission intensity in DNA-bound form while in free state its emission intensity is quenched by the buffered solvent medium. If another molecule competing for intercalation into the DNA-base pairs is added to the solution containing DNA-EtBr adduct, it will compete with EtBr and will tend to replace the later [25]. If the added molecule successfully replaces the EtBr and gets inserted into the DNA strand, the emission intensity of the EtBr will be reduced since the quantity of the DNA-bound and emissive EtBr has been reduced. On successive addition of the synthesized complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u0026nbsp;\u003c/strong\u003eto the solution containing DNA-EtBr adduct, its emission intensity was reduced on each addition. This showed that the complexes are able to compete successfully with EtBr for intercalation into the DNA base pairs as shown in Fig. 8 for complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e. This technique indicated that the complexes are more potent intercalators than EtBr and that the mode of binding of the complexes with DNA is intercalation as deduced from the previous techniques.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDNA-binding study using cyclic voltammetry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eChange in the concentration of an electro-active compound can be followed by cyclic voltammetry where the resulting current is changed with change in concentration. In this context, cyclic voltammograms of the complexes were recorded before and after adding variuos quantities of DNA. The voltammograms did suffer deminution in current on addition of DNA which indicated binding with the complexes as shown in Fig. 9. The diminution in current of the complexes on addition of DNA was used to calculate the binding constant of the complexes with DNA using plots shown in Fig. 10. The results of the four techniques on DNA-binding study are in harmony with each other.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 Molecular Docking Studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe binding interactions of the compounds \u003cstrong\u003e1-4\u003c/strong\u003e with DNA were assessed through molecular docking analysis, which allowed us to examine how these complexes interact with their target. Fig. 11 shows the best-docked conformations of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e. In all instances, the ligands bind to DNA\u0026apos;s major groove, with binding scores falling within the range of -6.5 to -7.4 kcal/mol. In all cases multiple conventional intermolecular hydrogen bonds are developed between the ligands and both strands of DNA base pairs showing a dual binding mode. The most effective among the docked complexes is compound \u003cstrong\u003e4\u003c/strong\u003e, with a docking score of -7.3 kcal/mol. It acts as four hydrogen bond acceptor through the oxygen of -OS(CH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e and -NO\u003csub\u003e2\u003c/sub\u003e groups. One hydrogen bond is formed with A:DA5 and three hydrogen bonds with B:DA17 and B:DA18 residues. It is also involved in \u0026pi;-donor hydrogen bonding through the phenyl ring and A:DG4 residue, \u0026pi;-sulphur interaction with A:DA6 and \u0026pi;-\u0026pi; T-shaped interaction with B:DA18 and DG10, indicating its strong binding affinity. Compounds \u003cstrong\u003e1-2\u0026nbsp;\u003c/strong\u003eshow equal binding affinity with a binding score of -6.9 kcal/mol. Compound \u003cstrong\u003e1\u003c/strong\u003e acts as two H-bond acceptor and interacts with A:DG2 and B:DC21. Further interactions of \u003cstrong\u003e1\u003c/strong\u003e with DNA include \u0026pi;-anion interaction with B:DT19, \u0026pi;-\u0026pi; T-shaped with B:DT20 and \u0026pi;-alkyl interaction with B:DG22. Compound \u003cstrong\u003e2\u003c/strong\u003e forms two conventional hydrogen bonds with A:DA6 and B:DA18, as well as a carbon-hydrogen bond with A:DT7, \u0026pi;-anion interaction with A:DG4, \u0026pi;-\u0026pi; T-shaped interaction with A:DC3 and B:DA17, and \u0026pi;-alkyl interaction with B:DT20. Compound \u003cstrong\u003e3\u003c/strong\u003e shows the least binding score of -6.5 kcal/mol and forms three hydrogen bonds with A:DC3 and B:DC21. The other binding interactions of \u003cstrong\u003e3\u003c/strong\u003e include carbon-hydrogen interactions, \u0026pi;-anion, \u0026pi;-\u0026pi; T-shaped, \u0026pi;-donor hydrogen bonds, and \u0026pi;-alkyl interactions. In summary, the molecular docking analysis reveals a robust binding relationship between these complexes and DNA, indicating their potential as promising anticancer agents.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.6 Anti-oxidant activity of complexes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnother activity of biological relevance is the ability of a complex to quench free radicals which are produced continuously in bio-systems. In order to ascertain this activity, the synthesized complexes have been treated with a free radical DPPH and the decrease in the concentration of DPPH indicated reaction between the two and quenching of the later. Plots in Fig. 12 show that with increase in concentration of complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e, their scavenging activity also increased. The activity of each of complexes\u003cstrong\u003e\u0026nbsp;2\u003c/strong\u003e and \u003cstrong\u003e3\u003c/strong\u003e was comparable to that of the ascorbic acid which was used as standard. The relative inhibition of the complexes showed that these complexes can be used to quench the free radicals as well.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.7 Anti-bacterial studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe in vitro antibacterial activity of the synthesized complexes against three Gram-positive strains (Bacillus subtilis, Micrococcus luteus and Staphylococcus aureus) and a Gram-negative strain (Escherichia coli). The activity was measured by calculating the area of zone of inhibition by the complexes and was classified accordingly as in the literature [12]. Table 3 lists the observed activity of the complexes where the highest activity was observed for complexes \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e4\u003c/strong\u003e (zone of inhibition 20 and 21) against Micrococcus luteus and Staphylococcus aureus. However, their activity against Bacillus subtilis and Escherichia coli was low (zone of inhibition = 17 mm for both complexes). Complexes \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e4\u003c/strong\u003e exhibited good activity against the rest of the bacterial species. Only complex \u003cstrong\u003e2\u003c/strong\u003e showed significant activity against \u003cem\u003eE. coli\u003c/em\u003e while moderate and low activities were exhibited against the rest of the species. The significant activity of complexes \u003cstrong\u003e1\u003c/strong\u003e and \u003cstrong\u003e2\u003c/strong\u003e might be due to the presence of bromo- and nitro-groups, respectively which are able to promote covalent and ionic interactions with cellular membranes and tissues of target bacteria. Anti-bacterial activity indicates potential biological relevance of the synthesized complexes.\u003c/p\u003e\n\u003cp\u003eTable 3: Antibacterial data of the synthesized complexes\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"38.775510204081634%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Bacterial strain\u003c/p\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003e\u003cem\u003eBacillus\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003esubtilis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.3265306122449%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eMicrococcus\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eluteus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.367346938775512%\"\u003e\n \u003cp\u003e\u003cem\u003eStaphylococcus\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eaureus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.306122448979592%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eEscherichia \u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eColi\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\" rowspan=\"5\"\u003e\n \u003cp\u003eAverage zone of inhibition (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.43298969072165%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.34020618556701%\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\" valign=\"top\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\" valign=\"top\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eCefixime\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\"\u003e\n \u003cp\u003e32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\"\u003e\n \u003cp\u003e31\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\" rowspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003eMinimum Inhibitory Concentration (mg/mL)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.43298969072165%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.34020618556701%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\" valign=\"top\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\" valign=\"top\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\" valign=\"top\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\" valign=\"top\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"18.91891891891892%\" valign=\"top\"\u003e\n \u003cp\u003eComplex 4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.864864864864865%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.324324324324323%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.27027027027027%\" valign=\"top\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eConcentration of each complex: 1 mg/mL in DMSO. \u003cem\u003eCefixime\u003c/em\u003e: 1 mg/mL.\u003c/p\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eFour new carboxylate complexes of copper(II) (\u003cstrong\u003e1-4\u003c/strong\u003e) have been synthesized with substituted phenyl acetic acids and pyridine. These were characterized using UV-Visible and FTIR spectroscopy and single crystal XRD. The FTIR study showed the bands which indicated their synthesis and attachment of ligands to copper ion. The biological significance has been explored via DNA-binding and antioxidant activity studied by UV-Visible and fluorescence spectroscopy, cyclic voltammetry and viscometry. All the four techniques yielded coherent results of the activity in line with the in silico findings. This indicated facile and potent DNA-binding activity of the synthesized complexes. The complexes also exhibited excellent anti-oxidant activity against free radical DPPH and the activity was comparable to that of the ascorbic acid. A further support to the biological potency of the synthesized complexes was given by their potent activity against gram positive as well as gram negative bacterial strains. This preliminary study showed that the synthesized complexes can have excellent biological potential.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary material:\u003c/strong\u003e Crystallographic data for the complexes \u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e reported in this paper have been deposited with the Cambridge Crystallographic Data Centre corresponding to CCDC #s 2068200, 2068201, 2068198 and 2068197, respectively. [Fax: +44 (1223)336 033]; e-mail: [email protected].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest statement:\u0026nbsp;\u003c/strong\u003eThe authors claim no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003e The data will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col start=\"1\" type=\"1\"\u003e\n\u003cli\u003eCirri D, Pratesi A, Marzo T, Messori L (2021) Metallo therapeutics for COVID-19. Exploiting metal-based compounds for the discovery of new antiviral drugs. Expert Opin Drug Discov 16:39-46\u003c/li\u003e\n\u003cli\u003eG\u0026uuml;rses C, Aktaş A, Balcıoğlu S, Fadhilah A, G\u0026ouml;k Y, Ateş B (2022) Synthesis, characterization, DNA binding and anticancer activities of the imidazolidine-functionalized (NHC)Ru(II) complexes. J Mol Struct 1247: 131350 \u003c/li\u003e\n\u003cli\u003eHack J, Crabb SJ (2022) Platinum-Based Chemotherapy \u0026lsquo;Rechallenge\u0026rsquo; in Advanced Non-ovarian Solid Malignancies. Clinical Oncology 34: E329-E344 \u003c/li\u003e\n\u003cli\u003eWang YR, Chen SF, Wu CC et al (2017) Producing irreversible topoisomerase II-mediated DNA breaks by site-specific Pt(II)-methionine coordination chemistry. Nucleic Acids Res 45: 10861\u0026ndash;10871\u003c/li\u003e\n\u003cli\u003eKolbeck PJ, Vanderlinden W, Gemmecker G et al (2021) Molecular structure, DNA binding mode, photophysical properties and recommendations for use of SYBR Gold. Nucleic Acids Res 49: 5143\u0026ndash;5158\u003c/li\u003e\n\u003cli\u003eBerdnikova DV, Sosnin NI, Fedorova OA, Ihmels H (2017) Governing the DNA-binding mode of styryl dyes by the length of their alkyl substituents \u0026ndash; From intercalation to major groove binding. Org Biomol Chem 16: 545-554\u003c/li\u003e\n\u003cli\u003eIqbal M, Haleem MA, Ali S et al (2021) Centro-symmetric paddlewheel copper(II) carboxylates: Synthesis, structural description, DNA-binding and molecular docking studies. Polyhedron 208: 115407\u003c/li\u003e\n\u003cli\u003eIqbal M, Ullah N, Haleem MA et al (2023) Synthesis, crystal structure elucidation, DNA-binding and micellization behavior of copper(II) carboxylate complexes. Results Chemistry 5: 100700\u003c/li\u003e\n\u003cli\u003eBruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.\u003c/li\u003e\n\u003cli\u003eSheldrick GM, (2015) SHELXT\u0026ndash;Integrated space-group and crystal-structure determination. Acta Crystallogr. A: Foundations and Advances 71: 3-8.\u003c/li\u003e\n\u003cli\u003eSheldrick GM, (2015) Crystal structure refinement with SHELXL. Acta Cryst C 71:3\u0026ndash;8 \u003c/li\u003e\n\u003cli\u003eIqbal M, Ali S, Tahir MN, Nawaz A, Anderson PA, Khan W, (2019) Mono- and poly-nuclear copper(II) carboxylates withflourous ligands: Synthesis, structure and improved properties, Inorg Chim Acta 498: 119177\u003c/li\u003e\n\u003cli\u003eEberhardt J, Santos-Martins D, Tillack AF, Forli S, (2021) AutoDock Vina 1.2.0: New Docking Methods, Expanded Force Field, and Python Bindings. J Chem Inf Model 61: 3891-3898.\u003c/li\u003e\n\u003cli\u003eTrott O, Olson AJ, (2010) AutoDock Vina: improving the speed and accuracy of docking with a new scoring function, efficient optimization, and multithreading. J Comput Chem 31: 455-461.\u003c/li\u003e\n\u003cli\u003eMorris GM, Huey R, Lindstrom W, Sanner MF, Belew RK, Goodsell DS, Olson AJ, (2009) AutoDock4 and AutoDockTools4: Automated docking with selective receptor flexibility. J Comput Chem 30: 2785-2791.\u003c/li\u003e\n\u003cli\u003eSanner MF, (1999) Python: a programming language for software integration and development. J. Mol. Graph. Model. 17: 57-61.\u003c/li\u003e\n\u003cli\u003eAccelrys S, Discovery studio modeling environment. Dassault Syst\u0026egrave;mes BIOVIA: San Diego, CA, USA 2017.\u003c/li\u003e\n\u003cli\u003eMushtaq A, Ali S, Iqbal M, Tahir MN, Ismail H (2017) Synthesis of a New Heteroleptic Copper(II) Complex: Structural Elucidation, DNA Binding and In-vitroAlpha Glucosidase Inhibition Studies. J Chem Soc Pak 39: 471-477\u003c/li\u003e\n\u003cli\u003eIqbal M, Ahmad A, Ali S et al (2013) Dimeric \u0026lsquo;\u0026lsquo;paddle-wheel\u0026rsquo;\u0026rsquo; carboxylates of copper(II): Synthesis, crystal structure and electrochemical studies. Polyhedron 50: 524\u0026ndash;531\u003c/li\u003e\n\u003cli\u003eDakua VK et al., (2023) Synthesis, crystal structure, Hirshfeld surface, and DFT studies of a Copper(II) complex of 5,5\u0026prime;-dimethyl-2,2\u0026prime;-bipyridine and 1,2,2-trimethylcyclopentane-1,3-dicarboxylic acid, Results Chem 6: 101050.\u003c/li\u003e\n\u003cli\u003eHussain A, AlAjmi MF, Rehman MT et al., (2019) Copper(II) complexes as potential anticancer and Nonsteroidal anti-inflammatory agents: In vitro and in vivo studies, Sci Rep 9: 5237\u003c/li\u003e\n\u003cli\u003eIqbal M, Ali S, Muhammad N, Sohail M (2013) Synthesis, crystal structures and electrochemical characterization of dinuclear paddlewheel copper(II) carboxylates. Polyhedron 57: 83\u0026ndash;93\u003c/li\u003e\n\u003cli\u003eBenesi HA, Hildebrand JH (1949) A Spectrophotometric Investigation of the Interaction of Iodine with Aromatic Hydrocarbons. J Am Chem Soc 71: 2703\u0026ndash;2707\u003c/li\u003e\n\u003cli\u003eSureshbabu P, Varghese B, Sujitha E, Sabiah S (2022) Syntheses, structure, DNA docking and antimicrobial studies of copper(II) complexes with diethylenetriamine and N-bidentate ligands. Inorg Chim Acta 536: article No. 120898\u003c/li\u003e\n\u003cli\u003ePhadte AA, Banerjee S, Mate NA, Banerjee A (2019) Spectroscopic and viscometric determination of DNA-binding modes of some bioactive dibenzodioxins and phenazines, Biochem Biophys Rep 18: article No. 100629\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-chemical-crystallography","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jocc","sideBox":"Learn more about [Journal of Chemical Crystallography](http://link.springer.com/journal/10870)","snPcode":"10870","submissionUrl":"https://submission.nature.com/new-submission/10870/3","title":"Journal of Chemical Crystallography","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"copper(II) paddlewheel complexes, structural study, DNA-binding, anti-oxidant activity","lastPublishedDoi":"10.21203/rs.3.rs-3960580/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3960580/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSynthesis, structural characterization and preliminary biological relevance of four new copper carboxylate complexes (\u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e4\u003c/strong\u003e) has been presented here. The complexes have been synthesized by direct treatment of the substituted phenyl acetate and pyridine ligands in aqueous medium. The complexes were stable indefinitely with excellent yield and were characterized using spectroscopic and single crystal XRD techniques. FTIR spectroscopy revealed the bridging bidentate coordination mode for the carboxylate moiety in accordance to the actual structure revealed by XRD. Moreover, UV-Visible spectroscopic and cyclic voltammetric studies helped in their characterization and yielded signals which were typical of the copper(II) complexes. Successfully solved single crystal XRD data showed binuclear paddlewheel structures for all the complexes with both copper ions linked through four OCO bridges of ortho-methoxy phenyl acetate (\u003cstrong\u003e1\u003c/strong\u003e-\u003cstrong\u003e3\u003c/strong\u003e) and ortho-methyl-meta-nitrophenyl acetate (\u003cstrong\u003e4\u003c/strong\u003e). The geometry around each copper was distorted square pyramidal where the apical positions are occupied by meta-bromopyridine (\u003cstrong\u003e1\u003c/strong\u003e), meta-methylpyridine (\u003cstrong\u003e2\u003c/strong\u003e) and DMSO (\u003cstrong\u003e3\u003c/strong\u003e and \u003cstrong\u003e4\u003c/strong\u003e) molecules. The complexes exhibited excellent DNA-binding activity majorly via intercalation as revealed by four experimental techniques in line with the in silico studies. Their anti-oxidant activity was also comparable to that of the ascorbic acid. Complexes 1 and 4 exhibited significant anti-bacterial activity against Micrococcus luteus and Staphylococcus aureus. These preliminary findings indicated the biological potential of the synthesized complexes.\u003c/p\u003e","manuscriptTitle":"Synthesis, structural elucidation, DNA-binding and anti-oxidant activities of centrosymmetric paddlewheel copper carboxylate complexes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-26 19:35:41","doi":"10.21203/rs.3.rs-3960580/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-03-08T19:55:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-02-22T13:27:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-22T13:27:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Chemical Crystallography","date":"2024-02-16T07:07:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-chemical-crystallography","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jocc","sideBox":"Learn more about [Journal of Chemical Crystallography](http://link.springer.com/journal/10870)","snPcode":"10870","submissionUrl":"https://submission.nature.com/new-submission/10870/3","title":"Journal of Chemical Crystallography","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8fd36f37-1c4b-47c9-b10f-692c7e021cbf","owner":[],"postedDate":"February 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-05-10T17:28:02+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-26 19:35:41","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3960580","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3960580","identity":"rs-3960580","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}